xalan-j/xsltc/xsl_choose_design.html (184 lines of code) (raw):
<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title>ASF: <xsl:choose> / <xsl:when> / <xsl:otherwise></title>
<meta http-equiv="content-type" content="text/html; charset=UTF-8" />
<meta http-equiv="Content-Style-Type" content="text/css" />
<link rel="stylesheet" type="text/css" href="resources/apache-xalan.css" />
</head>
<!--
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
-->
<body>
<div id="title">
<table class="HdrTitle">
<tbody>
<tr>
<th rowspan="2">
<a href="../index.html">
<img alt="Trademark Logo" src="resources/XalanJ-Logo-tm.png" width="190" height="90" />
</a>
</th>
<th text-align="center" width="75%">
<a href="index.html">XSLTC Design</a>
</th>
</tr>
<tr>
<td valign="middle"><xsl:choose> / <xsl:when> / <xsl:otherwise></td>
</tr>
</tbody>
</table>
<table class="HdrButtons" align="center" border="1">
<tbody>
<tr>
<td>
<a href="http://www.apache.org">Apache Foundation</a>
</td>
<td>
<a href="http://xalan.apache.org">Xalan Project</a>
</td>
<td>
<a href="http://xerces.apache.org">Xerces Project</a>
</td>
<td>
<a href="http://www.w3.org/TR">Web Consortium</a>
</td>
<td>
<a href="http://www.oasis-open.org/standards">Oasis Open</a>
</td>
</tr>
</tbody>
</table>
</div>
<div id="navLeft">
<ul>
<li>
<a href="index.html">Overview</a>
</li></ul><hr /><ul>
<li>
<a href="xsltc_compiler.html">Compiler design</a>
</li></ul><hr /><ul>
<li>
<a href="xsl_whitespace_design.html">Whitespace</a>
</li>
<li>
<a href="xsl_sort_design.html">xsl:sort</a>
</li>
<li>
<a href="xsl_key_design.html">Keys</a>
</li>
<li>
<a href="xsl_comment_design.html">Comment design</a>
</li></ul><hr /><ul>
<li>
<a href="xsl_lang_design.html">lang()</a>
</li>
<li>
<a href="xsl_unparsed_design.html">Unparsed entities</a>
</li></ul><hr /><ul>
<li>
<a href="xsl_if_design.html">If design</a>
</li>
<li>Choose|When|Otherwise design<br />
</li>
<li>
<a href="xsl_include_design.html">Include|Import design</a>
</li>
<li>
<a href="xsl_variable_design.html">Variable|Param design</a>
</li></ul><hr /><ul>
<li>
<a href="xsltc_runtime.html">Runtime</a>
</li></ul><hr /><ul>
<li>
<a href="xsltc_dom.html">Internal DOM</a>
</li>
<li>
<a href="xsltc_namespace.html">Namespaces</a>
</li></ul><hr /><ul>
<li>
<a href="xsltc_trax.html">Translet & TrAX</a>
</li>
<li>
<a href="xsltc_predicates.html">XPath Predicates</a>
</li>
<li>
<a href="xsltc_iterators.html">Xsltc Iterators</a>
</li>
<li>
<a href="xsltc_native_api.html">Xsltc Native API</a>
</li>
<li>
<a href="xsltc_trax_api.html">Xsltc TrAX API</a>
</li>
<li>
<a href="xsltc_performance.html">Performance Hints</a>
</li>
</ul>
</div>
<div id="content">
<h2><xsl:choose> / <xsl:when> / <xsl:otherwise></h2>
<p align="right" size="2">
<a href="#content">(top)</a>
</p>
<h3>Contents</h3>
<ul>
<li>
<a href="#functionality">Functionality</a>
</li>
<li>
<a href="#implementation">Implementation</a>
</li>
</ul>
<a name="functionality"></a>
<p align="right" size="2">
<a href="#content">(top)</a>
</p>
<h3>Functionality</h3>
<p>The <code><xsl:choose></code> element is used to determine one
course of action based on a series of tests. Each test is done inside an
<code><xsl:when></code> element. If a test succeeds, the body of the
<code><xsl:when></code> element is executed. If no tests fail then
a <code><xsl:otherwise></code> element can be used to specify a
default action:</p>
<blockquote class="source">
<pre>
<xsl:choose>
<xsl:when test="element-available('some-extension')">
...
</xsl:when>
<xsl:when test="function-availabe('saxon:nodeset')">
...
</xsl:when>
<xsl:otherwise>
...
</xsl:otherwise>
</xsl:choose></pre>
</blockquote>
<a name="implementation"></a>
<p align="right" size="2">
<a href="#content">(top)</a>
</p>
<h3>Implementation</h3>
<p>The <code>Choose</code> class places all <code>When</code> child-nodes
in a vector. The <code>Choose</code> class translates the "test"-attribute
of all <code>When</code> nodes (in strict order) and chains them together
in an if-else style. The expression that holds each test contains a true-
and a false-list. These lists are vectors of branch targets that should be
used if the test succeeds or fails, respectively. The first test's
false-list is pointed to the start of the next test (ie. if the first test
fails, then we run the next test). The last test's false-list points directly
to the code for the body of the <code><xsl:otherwise></code> element.
</p>
<p>Just as with the <code><xsl:if></code>-element, special care is
taken for the <code>element-available()</code> and
<code>function-available()</code> functions. These functions are evaluated at
compile-time (this can be done since all parameters for these functions are
literals) and the body of a <code><xsl:when></code> element is not
compiled if we know that it will never be needed at runtime.</p>
<p align="right" size="2">
<a href="#content">(top)</a>
</p>
</div>
<div id="footer">Copyright © 1999-2014 The Apache Software Foundation<br />Apache, Xalan, and the Feather logo are trademarks of The Apache Software Foundation<div class="small">Web Page created on - Thu 2014-05-15</div>
</div>
</body>
</html>